Method for manufacturing an embossed sheet comprising a ply of water-soluble material

ABSTRACT

The invention proposes an embossed sheet ( 10 ) comprising at least one ply ( 12 ) of tissue having an embossing pattern comprising at least one series of protuberances ( 18 ) formed projecting from one surface of the said ply ( 12 ) of tissue, and at least one ply joined to the said at least one ply ( 12 ) of tissue and located opposite the said surface of the ply ( 14 ) of water-soluble material,
         characterized in that the ply ( 14 ) of water-soluble material is joined to the said at least one ply ( 12 ) of tissue at the summits ( 18   a ) of at least part of the protuberances ( 18 ).       

     The invention also proposes a method for manufacturing such a multi-ply sheet ( 10 ).

RELATED APPLICATION DATA

This application is a continuation application of U.S. patent application Ser. No. 12/920,776, filed Sep. 2, 2010, now U.S. Pat. No. 8,506,756 which is a national stage filing based on PCT International Application No. PCT/FR2009/000231, filed on Mar. 4, 2009, which claims priority to French Application No. 0851455, filed on Mar. 6, 2008, each of which is herein incorporated by reference in its entirety.

The invention proposes an embossed sheet comprising at least one ply of tissue and at least one ply of water-soluble material.

The invention proposes more particularly an embossed sheet comprising at least one ply of tissue having an embossing pattern comprising at least one series of protuberances formed and projecting from one surface of the said ply of tissue, and comprising at least one ply of water-soluble material.

The ply of water-soluble material is prepared so as to form a impermeable barrier to liquids, microorganisms such as bacteria and viruses contained in these liquids.

The function called “impermeable” of the barrier formed by the water-soluble ply consists here in temporarily preventing the liquids from passing through the said ply.

Thus, the use of a ply of water-soluble material, in combination with at least one ply of tissue, serves to obtain a product comprising, on the one hand, the absorbent properties of the tissue ply and, on the other, the waterproofness procured by the ply of water-soluble material.

These properties are particularly advantageous for the use of a paper product as a facial tissue or as bathroom tissue, because the bacteria and/or viruses cannot be transferred to the user's hand.

Moreover, when the paper product is used as bathroom tissue, each of the various plies constituting the paper product is suitable for being dispersed in the water, when the product is discarded into the toilet, without the risk of blocking the pipes.

Document GB-B-1 185 227 describes such a paper product, for which the ply of water-soluble material is prepared by hot extrusion and is hot bonded to the tissue plies discharged from the extruder, so that the tissue plies partly absorb the water-soluble material which has not yet hardened.

However, such a manufacturing method is relatively complicated to set up, and this document does not specifically describe the connection between the ply of water-soluble material and each ply of tissue.

It is the object of the invention to propose a paper product comprising a ply of water-soluble material which is joined to at least one ply of tissue so that the product has the usual properties of such a paper product.

For this purpose, the invention proposes an embossed sheet of the type described previously, characterized in that the ply of water-soluble material is joined to the said at least one ply of tissue at the summits of at least part of the protuberances.

According to other features of the sheet according to the invention, taken separately or in combination:

-   -   the ply of water-soluble material is joined to the said at least         one ply of tissue by local dissolution of the ply of         water-soluble material, at the summits of the said at least part         of the protuberances, to which the ply of water-soluble material         is joined;     -   the surface of the ply of water-soluble material is suitable for         being dissolved for the joining of the ply of water-soluble         material to the said at least one ply of tissue;     -   the ply of water-soluble material is suitable for being         dissolved locally by a water-based liquid;     -   the liquid comprises water and an additive;     -   the liquid is water;     -   each of the said summits of the said at least part of the         protuberances is suitable for being humidified before the         joining of the ply of tissue to the ply of water-soluble         material, to cause the partial dissolution of the ply of         water-soluble material at the contact with the said summit of         the said at least part of the protuberances;     -   the ply of water-soluble material is joined to the said at least         one ply of tissue by adhesion of the water-soluble material to         the said summits of the said at least part of the protuberances;     -   the sheet comprises at least two plies of tissue each having an         embossing pattern which comprises at least one series of         protuberances oriented inwardly from the sheet and the ply of         water-soluble material is arranged between the said at least two         plies of tissue and is joined to each of the said two plies at         the summits of at least part of the protuberances of each of the         said two plies of tissue;     -   the ply of water-soluble material is based on an at least         partially hydrolysed polyvinyl alcohol;     -   the ply of water-soluble material is based on an at least 90%         hydrolysed polyvinyl alcohol;     -   the thickness of the ply of water-soluble material is less than         25 μm;     -   the ply of water-soluble material is embossed and comprises at         least one series of protuberances;     -   the ply of water-soluble material comprises perforations and/or         micro-perforations.

It is a further object of the invention to propose a method for manufacturing an embossed sheet according to the invention, comprising at least one ply of tissue and at least one ply of water-soluble material,

characterized in that it consists in embossing at least one ply of tissue to form protuberances on one surface of the said at least one ply of tissue and then in joining the ply of water-soluble material to the summits of at least part of the protuberances of the said at least one ply of tissue.

According to other features of the method, taken separately or in combination:

-   -   the summits of the protuberances of the said at least part of         the protuberances are coated with adhesive before the joining of         the ply of water-soluble material to the said at least one ply         of tissue;     -   the summits of the protuberances of the said at least part of         the protuberances are humidified before the joining of the ply         of water-soluble material to the summits of the protuberances to         cause a local dissolution of the surface of the ply of         water-soluble material upon its contact with the humidified         summits;     -   the surface of the ply of water-soluble material located         opposite the ply of tissue is humidified locally before the         joining of the ply of water-soluble material to the said at         least one ply of tissue;     -   the said surface of the ply of water-soluble material is         humidified at the summits of the protuberances of the said at         least one ply of tissue;     -   the ply of water-soluble material is embossed before its joining         to the said at least one ply of tissue;     -   the ply of water-soluble material comprises perforations and/or         micro-perforations which are produced before the embossing of         the ply of water-soluble material;     -   the method is suitable for manufacturing a sheet which comprises         at least one first and at least one second ply of tissue between         which the ply of water-soluble material is arranged, and the ply         of water-soluble material is joined simultaneously to the said         at least one first ply of tissue and to the said at least one         second ply of tissue during an operation for joining the plies.

Other features and advantages of the invention will appear from a reading of the detailed description that follows, for an understanding of which reference should be made to the appended figures in which:

FIG. 1 is a schematic representation of an embossed sheet according to the invention comprising two plies of tissue and an intermediate ply of water-soluble material;

FIG. 2 shows a section of the sheet shown in FIG. 1, showing the protuberances of the plies;

FIG. 3 shows a section of the sheet comprising a single ply of tissue and one ply of water-soluble material;

FIG. 4 shows a similar section to that of FIG. 2, showing an alternative embodiment of the invention, for which the ply of water-soluble material comprises protuberances;

FIG. 5 is a schematic representation of an installation for producing an embossed sheet according to the invention as shown in FIG. 3

FIGS. 1, 2 and 3 show a paper product 10 such as an embossed sheet comprising a plurality of superimposed plies 12, 14

The sheet 10 is, for example, a sheet of bathroom tissue or a disposable facial tissue.

In a first embodiment shown in FIGS. 1 and 2, the sheet 10 comprises two plies 12 of tissue and one ply 14 prepared from water-soluble material arranged between the two tissue plies 12.

In a second embodiment shown in FIG. 3, the sheet 10 comprises a ply 12 of tissue and a ply 14 prepared from water-soluble material.

It will be understood that the invention is not limited to these embodiments of the embossed sheet 10, which may comprise a larger number of plies 12 of tissue and/or a larger number of plies 14 of water-soluble material.

Furthermore, a ply 12 of tissue may comprise a group of plies joined together so as to behave like a single ply.

Each ply 12 of tissue is prepared in a conventional manner, for example by conventional wet pressing called CWP, and its basis weight is adapted to the use of the sheet, for example the basis weight of the tissue ply 12 is between 12 and 30 g/m².

The ply 14 of water-soluble material is prepared from a material suitable for being dissolved after prolonged contact with water. It consists of a plastic, preferably a polyvinyl alcohol (PVA) which is a polyvinyl acetate (PVAc), that has been hydrolysed to become water-soluble.

A modification of the hydrolysis rate of the ply 14 of water-soluble material serves to modify the time required for the dissolution of the ply 14 of water-soluble material. Thus, it is possible to adjust this hydrolysis rate according to the desired properties of the sheet 10.

Preferably, the hydrolysis rate of the plastic is higher than ninety percent (90%)

Another property of the water-soluble material used to form the ply 14 further consists in that the material is non-porous and is suitable for forming a sealed barrier to liquids, before its dissolution.

Thus, the liquids and microorganisms such as bacteria and/or viruses applied to one surface of the sheet 10 cannot be transferred to the other surface of the sheet which is, for example, in contact with the user's hand, thereby serving to ensure a hygienic use of the sheet 10, in particular when the sheet 10 is used as a facial tissue or bathroom tissue, as previously mentioned.

The thickness of the ply 14 of water-soluble material is preferably lower than 25 μm.

Finally, according to an alternative embodiment of the embossed sheet 10, the ply 14 of water-soluble material comprises perforations and/or micro-perforations.

These perforations and/or micro-perforations serve in particular to increase the absorption rate of the sheet 10 and to improve its flexibility.

The sheet 10 is an embossed sheet, that is at least one of the plies 12, 14 comprises at least one embossing pattern.

According to a common definition, embossing is a mechanical operation of deformation which modifies the relief of a sheet.

According to the embodiments shown in FIGS. 1 to 3, each ply 12 of tissue comprises an embossing pattern 16 which extends over part of the surface of the ply 12 and which comprises a plurality of protuberances 18 oriented inwardly from the sheet 10

Furthermore, according to these embodiments, the ply 14 of water-soluble material is flat, that is it does not comprise any embossing pattern

According to the embodiment shown in FIG. 4, the ply 12 of tissue and the ply 14 of water-soluble material each comprise an embossing pattern composed of a plurality of protuberances 18, 20.

Here, each ply 12, 14 comprises a single embossing pattern and the relief of the protuberances caused by the embossing is identical for the two plies 12, 14.

According to an alternative embodiment, at least one ply 12, 14 comprises a plurality of embossing patterns 16, forming for example a background pattern and a main pattern.

The height and density of the protuberances 18, 20 of a pattern 16 may be different from the height of the protuberances 18, 20 of the other pattern 16, thereby serving to procure for the sheet 10 desired properties of softness, absorption and flexibility.

Furthermore, here, the plies 12, 14 are joined together by a joining mode known by the designation points/points, that is, in such a way that the summits 18 a, 20 a of the protuberances of each of the plies 12, 14 are caused to coincide.

According to an alternative embodiment, not shown, the plies 12, 14 may be joined by the technique called “nested”, for which the protuberances are imbricated.

According to the invention, each ply 12 of tissue is joined to the ply 14 of water-soluble material at the summits 18 a of at least part of the protuberances 18.

According to a first embodiment of the invention, the joining of each ply 12 of tissue to the ply 14 of water-soluble material is carried out by bonding all or part of the summits 18 a of the protuberances 18 of each ply 12 of tissue to the opposite surface 14 a of the ply 14 of water-soluble material.

Preferably, the bonding takes place by depositing adhesive on all or part of the summits 18 a of the protuberances 18 before the plies 12, 14 are contacted with one another.

According to a preferred embodiment of the invention, the joining of each ply 12 of tissue to the ply 14 of water-soluble material is carried out by partial dissolution of the ply 14 of water-soluble material, at the summits 18 a of the protuberances 18.

The partial dissolution of the ply 14 of water-soluble material is obtained by locally applying a water-based liquid to the ply 14 of water-soluble material.

The water-soluble material has the cohesion, or the behaviour, of a solid when it is dehydrated, and the cohesion of a viscous liquid when it is hydrated, that is when it is mixed with water.

When the summit 18 a of a protuberance of the ply 12 of tissue is in contact with the partially dissolved zone of the ply 14 of water-soluble material, the summit 18 a absorbs part of the dissolved water-soluble material. The tissue and the water-soluble material are thereby mixed.

Then, the two plies are joined together by pressing and then by natural or forced dehydration so that the contact zones between the plies 12, 14 become joining zones between the said plies following the cohesion thereby created

According to a first embodiment, the product used to cause the partial dissolution of the water-soluble material is exclusively water, so that the ply 12 of tissue is joined to the ply 14 of water-soluble material exclusively by the quantity of water-soluble material that has been dissolved.

According to an alternative embodiment, the product used to cause the partial dissolution of the water-soluble material consists of a mixture of water and an additive such as adhesive, which serves to improve the joining of the ply 12 of tissue to the ply 14 of water-soluble material.

Furthermore, the quantity of liquid used to cause a local dissolution of the ply 14 of water-soluble material, is determined so that only the outer surface of the ply 14 of water-soluble material is dissolved, that is a central portion, in the thickness of the ply 14 of water-soluble material, is not dissolved. This serves in particular to preserve the impermeability function of the ply 14 of water-soluble material over its whole surface.

Such a feature of dissolution of the ply 14 of water-soluble material exclusively on the surface is preferably obtained by first humidifying the summits 18 a of the protuberances 18, so that the quantity of liquid that dissolves the ply 14 of water-soluble material is limited, and the dissolution occurs when each ply 12 of tissue is placed in contact with the ply 14 of water-soluble material.

The ply 14 of water-soluble material is thereby placed in contact with the bonding liquid for a limited period of time.

When the ply 14 of water-soluble material is arranged between two plies 12 of tissue, as shown in FIGS. 1 and 2, each surface of the ply 14 of water-soluble material is joined to a ply 12 of tissue according to the invention, that is, the ply 14 of water-soluble material is joined to summits 18 a of protuberances 18 of a ply 12 of tissue, which extends inwardly from the sheet 10, towards the ply 14 of water-soluble material.

By contrast, when the ply 14 of water-soluble material is joined to a single ply 12 of tissue, as shown in FIGS. 3 and 4, only one surface of the ply 14 of water-soluble material is joined to the ply 12 of tissue according to the invention, that is, the surface of the ply 14 of water-soluble material located opposite the ply 12 of tissue is joined to the summits 18 a of all or part of the protuberances 18 of the said ply 12 of tissue.

FIG. 5 shows an installation for producing a sheet according to the invention.

This installation is constructed here in order to produce a sheet 10 comprising a single ply 12 of tissue which is embossed, and comprising a ply 14 of water-soluble material which is flat, as shown in FIG. 4.

The installation comprises an engraved embossing roller 22 of which the convex outer cylindrical surface 22 a comprises a series of pins 24 formed in relief and of which the form or outer profile is identical to that which is to be obtained for each corresponding protuberance 18 of the ply 12 of tissue.

In a manner known per se, the ply 12 of tissue first passes between the first engraved roller 22 and an associated roller 26 to produce the embossing pattern of this ply 12. The associated roller 26 may have a rubber coating or similar, or optionally a rigid coating having a hardness lower than the hardness of the engraved roller 22.

The ply 12 of tissue then passes in front of the applicator roller 28 belonging to a coating unit 30, of known design, which deposits a bonding product on the summits 18 a of the protuberances 18.

The coating unit 30 serves to deposit the bonding product on all the summits 18 a of the protuberances 18, or on only part of the summits 18 a of the protuberances 18, in particular on the summits 18 a of the protuberances 18 which are the highest when the ply of tissue comprises a plurality of embossing patterns 16 having different heights.

According to the invention, and as previously described, the bonding product may be adhesive, water or a mixture of water with a binder, and is referred to below by the term bonding product.

In a manner known per se, the coating installation comprises an engraved roller 34, commonly called “anilox”, of which the cylindrical surface comprises cavities (not shown) which are suitable for being filled with bonding product, during the passage thereof in front of a tank 36 for then transferring the bonding product to the applicator roller 28.

The anilox 34 serves to transfer the bonding product in a predefined and controlled manner onto the applicator roller 28. This serves to limit the quantity of bonding product in motion.

The cavities of the anilox 34 are preferably such as to have a volume of between 3 and 40 cm³/m².

The ply 14 of water-soluble material is then placed in contact with the ply 12 of tissue.

Then, the two plies 12 and 14 pass into a “nip” between the embossing roller 22 and a roller 32, called marrying roller, to associate the plies 12, 14 by the pressure of the marrying roller 32 against the embossing roller 22.

Thus, the method for manufacturing an embossed sheet 10 according to the invention via this installation comprises a first step of embossing of the ply 12 of tissue, to produce at least one embossing pattern 16 consisting of protuberances 18 on one surface of the said ply 12.

This embossing step is implemented by the cooperation of the engraved roller 22 with the associated roller 26.

This method also comprises a step of joining the ply 12 of tissue to the ply 14 of water-soluble material, here by cooperation of the engraved roller 22 with the marrying roller 32.

According to the invention, the step of embossing the ply 12 of tissue is implemented before the step of joining the ply 12 of tissue to the ply 14 of water-soluble material. Moreover, also according to the invention, the bonding step consists in joining the ply 12 of tissue to the ply 14 of water-soluble material at the summits 18 a of the protuberances 18.

For this purpose, the coating installation 30 deposits the bonding product before the joining of the ply 12 of tissue to the ply 14 of water-soluble material.

Thus, when the bonding product is water-based, the ply 14 of water-soluble material is only locally dissolved when it is placed in contact with the ply 12 of tissue of which the summits 18 a of the protuberances 18 have been humidified.

This serves to limit and control the extent of the dissolution of the ply 14 of water-soluble material, so as to avoid weakening its properties excessively, particularly the impermeability properties.

According to an alternative embodiment of the method of the invention, the bonding product is applied to the ply 14 of water-soluble material, before its joining to the ply 12 of tissue.

The installation is then modified accordingly, that is, the coating installation 30 is arranged to apply the bonding product directly to the ply 14 of water-soluble material.

When the ply 14 of water-soluble material passes opposite the ply 12 of tissue, the latter has been formed to have the properties previously mentioned, that is, the material has been partly hydrolysed.

Furthermore, in the case in which the ply 14 of water-soluble material comprises perforations or micro-perforations, they are generally produced before the ply 14 of water-soluble material reaches the installation as described previously.

Preferably, the micro-perforations in the context of the present invention have a density lower than 150/cm² and their diameter is smaller than 1 mm.

Moreover, according to the embodiment of the embossed sheet 10 according to which the ply 14 of water-soluble material is also embossed, as shown in FIG. 4, the embossing is carried out before it is placed in contact with the ply 12 of tissue. For this purpose, the installation comprises an additional embossing unit (not shown).

The same applies for manufacturing the embossed sheet shown in FIG. 2, which comprises two plies 12 of tissue between which the ply 14 of water-soluble material is arranged.

The installation then comprises an engraved roller 22 and a coating unit 30 as described previously, associated with each ply 12 of tissue.

The ply 14 of water-soluble material is then placed opposite each of the two plies 12 of tissue, for it to be arranged between them.

Then, all the plies 12, 14 pass simultaneously in front of the matching roller 32 in order to associate the ply 14 of water-soluble material simultaneously with the two plies 12 of tissue.

The embossed sheet according to the invention thereby procures better temporary protection in comparison with a “conventional” sheet, that is one which does not comprise a ply of water-soluble material, and preserves conventional disintegration properties after use, that is, when it is discarded into the discharge lines of sanitary facilities.

The comparative table below shows the results of various measurements between a multi-ply sheet, for use as bathroom tissue, of which the design is called “conventional”, and which comprises three plies of tissue, and a multi-ply sheet according to the invention.

More precisely, the multi-ply sheet called “conventional three-ply paper” in the table comprises two outer plies of the CWP type and one central ply having a mechanical strength greater than that of the two outer plies.

The multi-ply sheet called “invention” in the table is manufactured according to the invention, and differs from the sheet called “conventional three-ply paper” only in terms of the central ply, which consists here of a ply of water-soluble material.

Conventional three-ply bathroom tissue Invention Thickness As such 0.354 ± 0.006 0.524 ± 0.030 (mm) In 12 plies 0.323 ± 0.003 0.491 ± 0.013 Absorption Capacity 9.3 11.8 (g/g) Time (s) 4 5 Disintegration (s) 8 20 to 25 Strength (N/m) — — MD dry 199 ± 7  >899 MD wet  4.7 ± 0.7** 8.0 ± 1.1  (12.9 ± 1.4)** CD dry 81 ± 5  281 ± 10  CD wet — — MD elongation % 19 25 to 73

It appears that all the measured parameters are improved, in particular the dry strength in the machine direction (MD), cross direction (CD), and the wet strength in the machine direction (MD) are improved. The elongation in the machine direction (MD) is also improved.

Moreover, the “disintegrability” function of the paper according to the invention is advantageously preserved. 

The invention claimed is:
 1. A method for manufacturing an embossed sheet comprising at least one ply of tissue and at least one ply of water-soluble material, the method comprising the steps of: embossing said at least one ply of tissue to form protuberances on one surface of said at least one ply of tissue; humidifying summits of the protuberances of at least part of the protuberances; and joining said at least one ply of water-soluble material to the summits of said at least part of the protuberances of said at least one ply of tissue to cause a local dissolution of the surface of the ply of water-soluble material upon its contact with the humidified summits.
 2. The method according to claim 1, wherein the summits of the protuberances of said at least part of the protuberances are coated with adhesive before joining the ply of water-soluble material to said at least one ply of tissue.
 3. The method according to claim 1, wherein the surface of the ply of water-soluble material located opposite the ply of tissue is humidified locally before joining the ply of water-soluble material to said at least one ply of tissue.
 4. The method according to claim 3, wherein said surface of the ply of water-soluble material is humidified at the summits of the protuberances of said at least one ply of tissue.
 5. The method according to claim 1, wherein the ply of water soluble material is embossed before its joining to said at least one ply of tissue.
 6. The method according to claim 5, wherein the ply of water-soluble material comprises perforations and/or micro-perforations which are produced before embossing the ply of water-soluble material.
 7. A method for manufacturing an embossed sheet comprising at least one first ply of tissue, at least one second ply of tissue, and at least one ply of water-soluble material arranged between said at least one first ply of tissue and said at least one second ply of tissue, the method comprising the steps of: embossing said at least one first ply of tissue to form protuberances on one surface of said at least one first ply of tissue; embossing said at least one second ply of tissue to form protuberances on one surface of said at least one second ply of tissue; humidifying summits of the protuberances of at least part of the protuberances on said at least one first ply of tissue and on said at least one second ply of tissue; and simultaneously joining the at least one ply of water-soluble material to said at least one first ply of tissue and to said at least one second ply of tissue to cause a local dissolution of the surface of the at least one ply of water-soluble material upon its contact with the humidified summits. 